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Re: Coelurus a maniraptoran (for how long?)
<By saying, "I know what a coelurosaur is, but becuase the other groups keep
changing in content, they must not be stable, so its a good reason to reject
their usage," is to say that taxa can only be inferred as content-bearing,
instead of by any other method. Or perhaps I'm barking up the wrong sauropod
This does not reflect the plasticity of relationship, or the
ability to define groups aside from plastic arrangement, which as you note
can change wildly. As Tom said, there will always be a Maniraptoriformes,
and a Maniraptora, and a Eumaniraptora. These are very stable groups. Their
contact [content(?) I think] is actually strongly constrained -- it is the
position of a few groups, 5 taxa each or so, that may shift in and out of
the defined group.
However, the multitude constituency stays the same. This provides
To paraphrase, certain animals are linked into a group on the basis of
supposed common ancestry.
The species constituting the membership of this group are determined by
analysis operating on certain physical attributes (characters). This
analysis assumes that the presence/absence of these attributes can ipso
facto demonstrate the common ancestry. The 'ipso facto' nature of the
conclusions arises from the use of selected logical principles (fewest
reversals, for one) which are supposed to be universally and inevitably
These physical attributes form a set (no single character can be the basis
for analysis) solely because the results of the analysis using them as a set
is the most compelling based on the universal and inevitable logical
principles, and not because of a functional or any other type of linkage.
Okay, so a sensu creates a group name. A sensu (compare 'sensai') is
defined as someone whose analysis is publishable as analysis and referred to
in discussions in later publications. In short, someone taken seriously.
The group members have most but not all of the same physical attributes.
The smaller the number of connecting attributes, the more likely the
'species' will be shifted into and out of the group.
I think you're arguing that the name has stability even if the membership
does not. However, the name is based on the sensu's analysis. If the
universal and inevitable principles are changed, or just modified, even the
sensu will reject his/her own prior analysis and the name will be
superseded. The name can also be superseded if a later sensu, working with
better data and a different catalogue of physical attributes, produces a
different named group. There are discussions of this occurring going on
The only thing that will not change are the physical attributes, assuming
that they have been correctly recorded. Note, though, that even the records
do change. I believe I've seen changes in the membership of a group when
animals are redescribed. Given the delicacy of the analysis, it seems
possible that a group name can be superseded if enough redescriptions cause
disappearance of the significance of the physical attributes on which the
analysis is based.
The composition of a group is in flux. So, potentially, is the existence of
I think. Correct me if I'm wrong.